The present application claims the benefit of priority from Japanese Patent Application No. 225478/2009, filed on Sep. 29, 2009, the contents of which are herein incorporated by reference in their entirety.
1. Field of the Invention
The present invention relates to a cellulose acylate film, a retardation film, a polarizer containing the film and a liquid crystal display device, especially a VA (vertical aligned)-mode liquid crystal display device.
2. Description of the Related Art
The display characteristics of liquid crystal display devices are being improved more and more these days, and in particular, it is known that, in a VA-mode liquid crystal display devices that is hopeful for large-sized TVs, two polarizers are arranged on the panel side and the backlight side of the liquid crystal display in such a manner that their absorption axes are perpendicular to each other, and in addition, an optically biaxial retardation film is arranged between each polarizer and the liquid crystal cell, thereby realizing a broader viewing angle, or that is, enhancing the display characteristics of the device.
As the retardation film of the type, recently, a cellulose acylate film capable of expressing excellent optical properties, concretely an in-plane retardation Re (nm) and a thickness-direction retardation Rth (nm) has become specifically noted and used as a retardation film in liquid crystal display devices. Among the cellulose acylate film, a cellulose acetate film is widely used.
As a compound that may be added to such a cellulose acetate film so as to increase Rth of the film, a retardation enhancer having a specific structure is disclosed (see JP-A 2004-109410). The retardation enhancer disclosed in this reference is a compound containing a keto-enol tautomerizable compound as its constitutive element and capable of forming a molecular complex; and as one example thereof, the reference discloses a compound having a 1,3,5-triazine ring-containing structure, especially a guanamine skeleton-having compound. As other compounds capable of being added to a cellulose acetate film to increase Rth of the film, disclosed are a retardation enhancer of a discotic compound (see JP-A 2001-166144, 2003-344655). The retardation enhancer disclosed in these references are discotic compounds and compounds having a structure containing a 1,3,5-triazine ring or porphyrin skeleton are exemplified therefor.